Rebounding typebars have always been a problem in the typewriter industry and the problem is more acute with electric typewriters which generally are operated at high speed. This problem is even more acute when a low cost typebar mechanism is utilized. Low cost typebar mechanisms generally do not lock in the rest position. In other words, any typebar may freely rebound from its rest position. Therefore, a returning typebar may easily rebound into the flight path of another typebar. Unless the energy of a returning typebar is substantially dissipated the moment it strikes the typebar support, the typebar is likely to rebound. If the typebar rebound is great, the typebar may collide with an adjacent typebar that is already in flight towards a printing point on a work sheet.
Collision of the typebars has been known to cause damage to the typebar parts and reduce the driving speed and impact force of the typebar. Variations in the impact force of individual typebars causes undesirable non-uniform type density and line of write.
If a typebar is in the repeat action mode or rapid typing is in process, and the typebar rebounds too high, it may not return to its rest position on the typebar support. If this occurs and a subsequent typing action begins, the driving force of the subsequent typing action is adversely affected. Consequently, the density of the printed character may be too light or too dark or the subsequent typebar may not engage the driving means properly and result in a non-print.
Improvements in the design of the typebar support have resulted in many designs that incorporated yieldable typebar receiving members.
One such design as shown in U.S. Pat. No. 3,384,217 to C. P. Anderson incorporates a fixed arcuate frame rigidly mounted to a typebar segment and includes a yieldable strip positioned in a slit in the arcuate frame. The yieldable strip is sandwiched between the frame and a rigid strip. An extension spring disposed along the length of the arcuate frame biases the yieldable strip radially inward. When a typebar returns to rest, the energy accumulated in the typebar during flight is absorbed and dissipated by the yieldable structure of the arcuate frame of the typebar support.
Another such design as shown in U.S. Pat. No. 2,903,119 to A. D'Onofrio, et al, includes a pair of arcuate interconnected elements pivotally supported on a pair of arms that are rigidly mounted to a frame. As a typebar returns to rest, it initially strikes the first element and then the second element. The energy accumulated in the typebar during flight is partially dissipated as the typebar strikes the first element and thereafter progressively absorbed until it strikes the second element at which time the typebar energy is fully dissipated.
A third such design as shown in U.S. Pat. No. 3,554,336, includes a thick plastic tape suspended at its ends by leaf springs and pins to provide a support for the typebars at rest. As a center typebar returns to rest on the support, it deforms the plastic tape and also twists the leaf springs. Therefore, the relative movement of the typebar support in relation to the typebars is increased and the attenuating effect of the typebar support is improved.
The typebar supports of the prior art all include arcuate yieldable members supported by rigid arms. This construction is costly in that a complicated structure is required to make the arcuate member yieldable. Furthermore, the total energy of the returning typebars in the prior art is absorbed in the arcuate member and not the entire support structure.
The present invention is an improvement over the typebar supports of the prior art in that the mounting of the typebar support and most of the yielding of the typebar support occur about one common point. The foregoing prior art structures do not provide a structure that is mounted and yields about a common point.
In other words, the present invention includes a rigid arcuate member with a yieldable pad mounted thereon. The arcuate member is supported by rigid arms that are rockably mounted to the frame.
The mounting and the the rocking of the typebar support about a common point allows for a less costly construction in that the portion of the typebar support on which the typebars rest does not require any complicated structure for yielding.
The energy of the returning typebar in the present invention is partially dissipated in the yeildable pad on the typebar support. The greatest amount of energy is dissipated when the entire support structure including the support arms is urged to rock as the typebars impact the support. Dissipating the energy of the returning typebars throughout the entire support structure including the support arms allows a more economical, efficient and a simplified construction to be used.